Conditioning paper-making stock



April 5, 1960 c. L. CLARK CONDITIONING PAPER-MAKING STOCK 2 Sheets-Sheet l 7 Filed April 21, 1953 INVENTOR i tw in! ATTORNEY April 5, 1960 c. CLARK CONDITIONING PAPER-MAKING s'rocK 2 Sheets-Sheet 2 Filed April 21. 1953 INVENTOR Car/e700 L. C/or/r y 0.4;! MAW ATTORNEY 2,931,503 CONDITIONING PAPER-MAKING STOCK Carleton Leggett Clark, North Tarrytown, N.Y., assignor,

by mesne assignments, to Clark & Vicario Corporation, Bronxville, N.Y.,'a corporation of New York Application April an 1953, Serial No. 350,087

12 Claims. 0.209-211 This invention relates to the preparing of paper-making stock to ready it for the paper-making machine and to improve its condition to be handled by that machine. 1

It has heretofore been proposed to improve its handleability by de-aerating it, sometimes referred to as degasifying it. This is accomplished by atomizing the pumpably fluid stock while subject to the effect of substantial vacuum, collecting a pond of de-aerated stock iffid States Patent F ICC the hydrocyclone is maintained under the efiect of vacuum so it can be returned advantageously to the de-aerating station. And another object is to make it possible to;

pass less than the. full volume of the stock to the paper machine throughthe de-dirting hydrocyclone and thus reduce the power requirements.

Some of the features of this invention contributing to the realization of these objects comprise the means whereby the effect of vacuum is maintained on the stock both while it is treated in the hydrocyclone station and afterdirt-poor-but with both flows being well de-aerated;

while still under the effect of vacuum and then conducting it to the paper-making machine. Such a proposal has been patented in the patent to DeCewNo. 2,571,219 dated October 16, 1951. It has also been proposed to clean or to de-dirt the stock prior to supplying it to the papermaking machine. This proposal has been carried out by treating the stock in a hydrocyclone to divide the stock into two fractions of which one is acceptable substantially dirt-free and thus clean stock, while the other has the dirt concentrated in it and is called rejected stock. One such proposal has been patented in the patent to Samson, et al.--No. 2,377,524, dated June 5, 1945,

while another such proposal hasbeen patented in the patcut to FreemanNo. 2,312,706, dated March 2, 1943.

Such centrifugal separating devices are characterized in that as 'a result of pressure on a tangential feed thereinto, vortices are said to be set up therein. The liquid body in the centrifugal separator is given a vortically spinning movement with inner and outer layers, in which outer layers are segregated coarser or faster settling solids, while in the inner layers are segregated the fine or slower settling solids. The devices of these two patents both comprise a hydrocyclone characterized in that two vortices are said to be set up therein. One

vortex discharges through the apex of the conical part of the cyclone and is called underflow, while the other vor-r tex discharges through a vortex finder in the base of the hydrocyclone and is called overflow. The dirt-free acceptable fraction is discharged as overflow while the dirtrich and rejected fraction is discharged as underflow.

In such a dirt-extracting hydrocyclone with its oppositelydirected axial discharges, an air-core is formed that passes completely through the hydrocyclone, and this aircore seems to aerate toan appreciable extent the stock while it is being cleaned. Since the centrifugal forces set up in such a hydrocyclone are considerable, the infeed pressures that have to be used are high. This means that a large amount of power is consumed in forcing through the de-dirting hydrocyclones the very large voland the means for continuously recycling the acceptable de-dirted deaerated stock from the hydrocyclone station back to the de-aerating station whereby the acceptability of the, stock in the major flow from that station is progressively improved until a maximum is reaced.

The objects of this invention, and perhaps others that appear as this specification proceeds, are realizable in an embodiment of this invention having an enclosed tank provided with meansfor subjecting the tank to vacuum-induced significantly reduced pressure into the at'-.

mosphere of which tankpumpable papermaking stock is atomized and then falls to join a pond of so-treated stock collected in the bottom of the tank on which a constant liquid-level is maintained. De-aerated or degassed stock then flows down a major fiow discharge pipe having a barometric leg to a pump. The entrance to that pipe is surrounded by a submerged weir-edge that holds back settled solids that have settled from thestock before it reaches the weir-edge to overflow it. The discharge pipe and the weir-edge is preferably shielded from" v settling solids in the stock. From that part of the tank outside of and below the, weir-edge there is drawna minor flow of stock'in which settled solids such 'as sand; and other fast-settling dirt is concentrated, is drawn off:

and forcibly fed to hydrocyclones in a hydrocyclone station, the interior of which hydrocyclones are maintained under the effect of vacuum so that'the-stock being.- treated therein does not become substantially re-aerated..

Underfiowed stock from the hydrocyclones being dirtrich is discarded, while overefiowed stock from the -hy-f drocyclones being both de-aerated and dirt-poor is recycled to the de-aerating station.

The best embodiment of the invention now known to.

me isillustrtated in the accompanying drawings; -This has been selected for illustrative and not for limiting pur- Figure 2 shows a vertical longitudinal sectionalj view" through the de-aerating station or tank. Fig. 3 shows a transverse sectional. view taken along the line 3--3 in" Fig. 2.- Fig.4 shows a vertical sectional viewthrough' a hydrocyclone-usable in practicing this invention.

Since the foundation of this-invention is based on'the paper-stock de-aerating or de-gassing station 10, that .will

be described first. In it there is an enclosed zone, such as'a cylindrical tank or stock receiverand de-aerator 11, to the top of which is connected a vacuum header 12 connected by a line or conduit 13 to a vacuum pump station 14 having an air-discharge 15 and a water-discharge 16. A suspension of paper-making stock to be treated comes into the tank ll'through' a primary'stock: header 17, from whence it passes through a plurality; of inlet pipes numbered similarly as 18, each leading- ,to an atomizing spray nozzle 19, hereinafter described; in more detail, for atomizing the stock into the vacuum Patented Apr. 5, 1960;;

induced significantly reduced pressure in the atmosphere 2 of the tank 11. The stock, so subdivided into tiny or miniscule droplets, is de-aerated and de-gassed by the vacuum, and falls as mist or fog to collect as liquid in the Bottom of the tank as apond thereof, having a maintained' liquid-level 21?. at an elevation substantially just below the axialline or middle of the tank; Vacuumtreated stock then fiows from the bottom of: thetank through main flow stock discharge outlet. 24" and down a barometric drop leg 25 (ShOWll-IflilCECfdIP diameter in Fig. I and-thusbeing merely illustrative) to a centrifugal orf'an pump 26 andthenthrough avalved pipe 27 to the head box 28 and then onto-'thewire" 29 of a paper.- making machine'SiI.

The tank 11 is supplied with stock to he treated, as follows: New stock comes into the system through a pipe 32 and is mixed ahead of afan or centrifugal pump- 33' with white Water drawn from thewire pit 34 through an pipe 35; The white water is used to: dilute the stock:

coming in through pipe 32 because the vacuum treat-- ment operates more effectively if the stock is dilutedand thus subject to intense atomization; The diluted stock from the stock pump 33 is forced through pipe 36 to pass selectively either through the hand operat'ed: valve.

37 or through the automatically controlled valve 38- to: primary stock header 17. Operation is usually through the latter because it is important to control the. constancy of the liquid-level 21- in the tank 11', and this is accomplished by the'automatic: valve. This also pro.- vides an assured constant delivery: ofi stock: from the. tank' 11. through the main delivery pipe. 25 to=the:paperz making machine 30.

The preferred construction of the atomizing. nozzles: 19 and their cooperating elements, is shown in. patent; application Ser. No. 259,248 filed November 30, 1.951,. by'Cl'arket al., now Patent No. 2,642,950.

Briefly stated, each nozzle has. a. cylindrical body 43 to: whichstock is fed tangentially throughfeed-pipe' 44-. The stock is swirled around in the cylindrical body' of: the nozzle at great speed, and then issues or is. ejectedv from: each of two oppositely directed nozzles: 45 and 46" is reinforced by its bottom marginalfiange 48.. Another.

suchsurface is the interior face. of the tank: 11. against which the oppositely directed nozzlesimpinge ejected atomized stock; Such forced impingement aids in the further atomization of the stock; To effect substantially; complete de-aeration of the stock, thetvacuum-inducedi reduced pressure in the tank. must bethe'resultof a=very high vacuum, preferably asset forth in the patents: and applications mentioned herein; But ifless." complete dc. aeration will do, much less vacuum is needed.

Surrounding the entrance to the main; stock discharge outlet" pipe 24 is an endless upstanding weir presentingaweir-edge 50, and thereabove, but well below the" liquid-level 21 in the tank is a shield or baffle: 51, pref; erably' dome-shaped or umbrella-like and havingja de pending peripheral flange 52 preferably-having a vent 72:

int thex'top thereof for inducing flowtherethrough. The baffle has extent considerably greater than that of the- Weir-edge" 50, as. can be seen from the drawings. In.the bottom of the tank, adjacent the main dischargepipe 24, but on, the opposite side of the weir-edge 50 therefrom: and also beneaththe shield 51,. are. a plurality of minor tTow'stockr outlet: pipes 53, similarly referenced, leading.

to; pipes. 54. merging into at barometric" leg: drop pipe 55 flowing the weir-edge into the main flow outlet pipe 24. These pipes may be'valved as shown, if desired.

These minor flows'of stock in which contaminants are more or less concentrated and while still under the effect of vacuum and thus'de-aerated, are drawn to the fan or centrifugal pump 56 and from there forced through pipe up of a plurality of similar hydrocyclones eachnumbered 60, to each. of. which stock. from the pipe 57 isforcibly supplied'tangentially to theihydrocyclone through pipes 61. 58 are merely representative of a number of such devices operating on the principle of' centrifugal and centripetal action that results iILthC separation of one type of liquidsuspended solids from another. For the purpose of illustration, there has been chosen that type of hydrocyclone shown in the patent to Samson et al., No. 2,377,524,

but other types can be used although this is the preferred type; Such a type-is shown in Fig; 4 in vertical sectional view; In-that showing, thehydrocyclone has a cylindrical portion 63 from which depends a conical por tion 64 that terminates in an apex discharge outlet 65 leading to a spray-receiving expansion chamber 66 into which the apex discharge is whirlingly sprayed from thehydrocyclone. Chamber 66 has an outflow pipe 67- for ta'ppingolf of'gas or air pressure along with some liquid while the main flow of the apex discharge stock fallsdown pipe 7-7". Thecylindrical portion 63 has a. base closure- 70' through which extends abase discharge outlet pipe 71', sometimes called avortex-finder. The overfiow=through pipe 71* could also betreated'in-an expansion chamber 66"; if desired;

In'such a hydrocyclone, the pump56 impels its forced feed tangentially into the cylindrical portion 63 Where it' sets up'centrifugal forces many times more powerful than gravity which in turn set up reaction centripetal forces. The result is that two similar directed spinning vortices are thus established and maintained in the hydrocyclone by the pumped feed and more rapidly settlingliquid-suspended solids are segregated and discharged as underfiow through the apex discharge 65, while the slower settling suspended solids are segregated and discharged as overflow through the vortex-finder 71 at the base of the generally conical device. made use of in this invention to de-dirt or clean the deaerated' dilute paper-making stock fed to' it,- namely tosubstantially' rid that stock of sand, grit, specks, and other contaminants, the dirt-rich and unacceptable fraction going out through the apex discharge while the dirtpoor and cleanfraction going out through the base. dis; charge. or vortex-finder 71.1 The primary acceptedsstoch from hydrocyclone station 58 is flowed through pipe 7-3: toa secondarystockheader:75, andfrom thence through,

pipes 76. and associated nozzles 19 to be recycled. and re.-atomized into the de-aerating tank 11. Undersome conditions, the nozzles 19 need not be used on this recycled stock. Rejected or unacceptable stock from the apex dischargeof'the hydrocyclones is conducted through barometric drop legs77 to bedelivered in submergence into a pond 78 of such stock, forming primary rejected stockorrejects, held. in a seal, basin 79. By having the rejected stock, such,stock is drawn oft fromthe basin79 throughpipe 80- by; fan. pump 31, and forced. through pipe 82 to a secondary hydrocyclone station illustrated The .hydrocyclones' of. the derdirting station These devices are only by single hydrocyclone 85, that is in all respects like the other hydrocyclone heretofore described, so the details thereof will be given the same reference numerals but primed. Here in hydrocyclone 85, the primary rejected stock is re-cleaned to reclaim some of its fibers. The stock that becomes re-cleaned and dirt-poor is acceptable as secondary accepted stock and conducted as'overflow through pipe 86 to join the primary accepted stock in pipe 75 for re-introduction and re-atomization in the tie-aerating tank 11. Rejected or stock that is still dirtrich is sprayingly discharged as undertlow through the apex discharge into spray-receiving expansion chamber 66"leading to barometric drop leg 90 terminating in subm'ergence in a pond 91 of similar stock held in a seal basin 92. v

Returning now, for a moment, to hydrocyclone station .58, and particularly to the expansion chamber 66 on the apex discharge of each hydrocyclone: its purpose is to permit the drawing ofl near its top through pipe 67, of any air or gas entrained in the stock being sprayed into that chamber. The pipe 67 conducting gas and some liquid, leads to a gas separation tank 93 which it joins at substantially the middle elevation thereof, that also has a barometric leg 94 whose end is submerged in the pond 78 in seal basin 79 and that also has a gasoutflow pipe 95 in its top that leads to the pipe 13 connected with the vacuum pump 14. The purpose of this separating tank, that is much larger than the expansion chamber 66, and is located between the expansion chambers 66 on the apex discharges of the hydrocyclone 60 and the vacuum lines 95 and 13, is to further separate air or gas from the stock suspension, so as to minimize the carrying of I such suspension into the vacuum system. The second hydrocyclone station has a similar but secondary gas separation tank 96 for a similar purpose, with a barometric drop leg 97 leading to the pond 91 in the seal basin 92 from which its secondary rejects flow to discard, and

1 a pipe 98 from its top leading to the vacuum line 13.

The degree of vacuum operating on the primary hydrocyclones 60 is controlled by valve 100 in pipe 73 through which primary accepted stock flows to the de-aeration -'tank 11, while valve 101 in pipe 86 controls the vacuum operating on the secondary hydrocyclones 85. Control is important because the accepted stock from the hydrocyclone is drawn to the tank 11 by means of the highvacuum maintained therein, and these valves regulate the sucking power of that vacuum. Valve 102 in pipe 95 from the separator 93, and valve 103 in pipe 98 from the separator 96 similarly regulate the eflect of vacuum in line 13 in its operation of those separators. All pipes are valved-to give ample controls.

Operation- Diluted paper-making stock is pumped through pump 33 and pipe 36 in quantity controlled by automatic valve 38 through primary stock header 17 and the plurality of inlet pipes 18, each connected to an atomizing nozzle element 19 that swirlingly sprays atomized stock into the de-aerating tank 11 against either the impingement baffle plate '47 or the interior periphery of the tank, as the case may be, from whence the atomized stock in the form of fog or mist descends to and is collected in a pond 20 thereof in the bottom of the tank that has a controlled liquid-level 21. The interior of the de-aerating tank is under the effect of a high vacuum eflected by vacuum pump 14 through vacuum line 13'that is connected with vacuum header 12 with the interior of the tank. The atomized stock impinged against the impingement surfaces while under high vacuum, is de-aerated or degassed substantially completely, but it still has a certain content of dirt or other such solid contaminants.

A major flow of the de-aerated stock in the pond thereof 20 overflows the endless weir-edge 50 surrounding the main flow stock discharge pipe 24 and passes through 25 to a pump 26 for delivery to the head-box 280i a papermaking machine. But between the weir-edge 50 and the ends of the tank 11, there is sedimentation taking place in the pond of stock of certain faster settling contaminants such as sand, grit, and so on. In other words, there is a substantially high concentration of settled contaminants outside the weir-edge, so that stock overflowing the weir-edge and passing through the main flow discharge 24 is acceptable cleaned and de-aerated stock.

The fractionlof stock that is dirt-enriched or in which dirt has settled outside the weir-edge 50 is tapped off, so that a minor flow of stock from the pond thereof, by

passing through two or more draw-off minor flow or aux iliary pipes 53 and conducted through pipes 54 to a pump 56 for delivery through pipe 57 to a primary de-dirting or hydrocyclone station 58, while still under the effect of vacuum so that a minimum of air gets back into the stock being so transported. This exclusion of air must continue during treatment of the dirty minor flow of stock in the 'de-dirting hydrocyclone station. This station is made up of a plurality of hydrocyclones of which the one shown in Fig. 4, is an example. The dirty stock is forcibly and tangentially fed to the cylindrical part 63 of the cyclone while the slower settling suspended solids move into the inner vortex to issue from the base. of the hydrocyclone through the vortex finder 71. The faster settling solids issue from the hydrocyclone through the apex discharge 65, so we have here a fractionation of the stock into a dirt-poor or clean fraction of acceptable stock overflowing through the vortex-finder and a dirt-rich or concentrated dirty fraction of rejected stock underfiowing through the apex discharge.

But in the normal operation of such a hydrocyclone open to the atmosphere, an air core is formed extending between the axially aligned outlets of the hydrocyclone. This results in aeration of the suspension being treated. However, aeration of the stock must be avoided because the object of this invention is to produce stock that is both de-aerated and de-dirted. So the formation ofthe usual air core must be prevented. This is accomplished by keeping both discharges from the hydrocyclone under the eifect of vacuum, namely, by making the apex discharge pass through a barometric'drop leg 77, and maintaining the base or overflow discharge 71 and its pipe 86 also under the efl'ect of vacuum through pipe 73 to the tank 11. Accepted cleaned and de-aerated stock from pipes 71 is recycled to the tie-aeration tank 11 through header 75, for re-treatment therein to rid'it of air that may have inadvertently gotten into it since it left that tank for its de-dirting treatment.

. Rejected dirty stock that flows down the barometric legs77 is caught in the pond 78 in the seal: tank 79. This dirty stock is again treated to further'de-dirt it by sending it to a secondary hydrocyclone station 85 wherein it is" again treated just as it was in the primary hydrocyclone station 58. Secondary accepted stock flows through pipe 86 toheader for re-treatment in the de-aerating tank 11, meanwhile having air excluded therefrom by being maintained under the eifect of vacuum during its hydro- ,v cyclone de-dirting treatment. 7 Secondary rejects from the isv extracted by pipfe- 67 through which-it is drawn to-gas separation. tank 93 from which such air issucked through piperj-sto the. vacuum line I: and any stock therein flows downwardly through a barornetric leg 94 to the seal tank 79 This same refinement treatment is added to the secondary'hydrocyclone station 85; The degree of vacuum operating on the hydrocyclone stations is controlled by the valves 100 and iii-1 respectively. The degree of vacuum operating on-the tie-aeration tank 11 is controlled by the character and operation of the vacuum pump station 14.. In the de-aeration. tank 11, there is provided a shield 51. over the weir-edge St to prevent settling solids from settling into the main flow discharge by deflecting them into another part of the tank. Vent 72 is forin ducing some-flow of stock through the shield to prevent hang up of stock on the underside of the shield.

From 10%? to ofthe total flow passing through the de-aerating tank 11 is removed through the minor flow or auxiliary stock outlets. However, because of" the settling out and accumuiation of the stock-contaminating solids, this 10% to 20% of the total flow contains 50% or even more of the total amount of solid contaminants in the entire flow. Thus 50% or more of the solid contaminants or dirt-of the stock is removed by pumping only 10% to 20% of the total fiow through the hydro cyclones, This means a significant saving in power over pumping. all of the very large volumes of stock fiow through the 'de-dirting hydrocyclones. It is surprising how the contaminant solids tend to settle or sediment in the area of the bottom of the tie-aeration .t-ank outside the. weir-edge 56. For example, in a de-aerating,tankv 6} in. diameter wherein the liquid-level is maintained at above. the. center of the tank, the velocities of the suspension moving horizontally toward the main flow discharge outlet 24, increase from the order of 0.15 feet per. second at either end of thetank to velocities ofthe order of 4 to 5 feet per second at the main outlet. Be-

- cause of these low velocities and relative quiescence, there is a significant settling to the bottom of the tank of the solid contaminants that are heavier and thus faster settling than the paper-making fibers themselves. So the intercepting of them in a minor flow from the tank and de-dirting that minor flow in a hydrocyclone station while maintained under the effect of vacuum is a major feature .i this invention; 7

.Technical effects inherent in the apparatus when in operation and realizable by the practice of this-invention comprise (l) maintaining aconstant sub-atmospheric pressure on the apexend of the hydrocyclone in order to produce a constant rate of rejectable fraction discharge.

and hence a constant cleaning efficiency; (2 maintaining a constant suction head and liquid submergence on the secondary hydrocyclone supply pump 81 which is handling.

the diluted reiectablc fraction to the secondary hydro.-. cyclone station 85 in order to maintain. a constant feed pressure; and-volume to that secondary hyrocyclone station; (3) maintaining a constant rejcctable fraction discharge rate and pressure as well as a constant feed pressure to the secondary hydrocyclone station whereby there is eliminated possible fluctuations in the basic weight of the paper made from the primary'hydrocyclone station acceptable fraction, which basic weight might otherwise varydue tovarying pressures; (4-) preventing atmos pheric air from entering in. at the apex end of the hydrocyclones; and (5) removing. whatever portion. of. the free air that is discharged. through the apex end of. the hydrocycio'ne along with reiectable fraction.

As'this invention may be embodied in several. forms without departing fi'om'the spirit or essential character istics thereof, the present embodiment is therefore illustra tive and not restrictive, since the scope of the invention. isdcfined in the appended claims rather than by the description precedinglhem, and all changes that fall within the met'es and-bounds of, the claims or. that form their j the undcrflow of the hydrocy'clones.

8 functional as well as conjointly cooperative equivalents, are therefore intended tobe embraced by those claims.

I claim: p 1. The continuous process of dc-gassing andde-dirtingpaper-making stock, which comprises establishing and maintaininga confined zone under vacuum-induced significantly reduced pressure, atomizing pumpable paper stock thereinto to encounter the de-gassing effect of the re.- cluced pressure while in atomized condition, collecting a pond of so (lo-gassed stock, maintaining a substantially constant liquid-level thereon, withdrawing a major how of the stock from the pond over an endless weir-edge, maintaining stock; in the pond beyond the weir-edge sufficiently quiescent to effect sedimentation of suspendeddirt therein, withdrawinga minor flow of such sedimented stock from anelevation lower than the weir-edge and from a point ahead of the weir-edge, forcibly supplying; tangentially to a de-dirting hydrocyclone such minor flow;

of (lo-gassed but dirty stock while still under the effect ofvacuum, dischargingly underflowing dirt-enriched stockirorn the hydrocyclone, dischargingly overflowing dedirted stock from the hydrocyclone while still dc-gassed, and returning at least some of the latter to the confined, zone, the stock supplied to the hydrocyclone being under. pressure while both discharges from the hydrocyclonev are maintained under the effect of vacuum for minimizing; entrainment of air into-the stock being treated in the hydrocyclone.

2. The. process according to claim 1, with the addition.

of shielding the'point of discharge of the major flow from. suspended solids descending inthe pond. I

3. The process according to claim 1, with the addition that at least one discharge from the hydrocyclone is. delivered into an expansion zone connected with a source of vacuum.

4. The process according to claim. 1, with the addition that theunderflow discharge from thehydrocyclone' is treated by passing it throughan expansion zone from.

which entrained gas is removed by vacuum and stock is passed to the atmosphere through a barometric leg.

5. The process according to claim 4, with the addition that stock from the barometric leg is re-subjected significantly reduced pressure, means for: atomizing pumpable paper stock into the tank, meansfor: maintaining a substantially constant level pond of stock inthe. tanlo.

a stock-discharge pipe in the bottom of the tank through which a major flow of treated stock passes, an endless weir-edgeencircling the entrance to the discharge pipe,

conduit. ineansfor withdrawing aminorflow of stock from-i.

the pond. at an: elevation lower than the weir-edge and from a point ahead of the weir-edge, a plurality of do: dirting hydrocyclones having an overflow. of de-gassed de dirted stock, means for forcibly supplying tangentiallyto. the hydrocyclones such minor flow stock, and a corrduit for returning such overfiowed stock to the tank, whereby stock sooverflowed is drawn back into the tank by the vacuum therein.

7:. Apparatus according to claim 6, with the addition of shielding means-in the tank for deflecting solids settling in the pond away from the discharge pipe;

: 8'. Apparatus according to claim 6, with means for maintaining the. effect of vacuum on both the overflowand 9; Apparatus according to claim 6, with an expansion chamber through which is passed at least one oi} the overflow and the underflow from the hydrocyclones and means connecting that chamber with a. source of vacuum.

10;. Apparatus according to claim 9 with a barometric leg connected. to the expansion chamber, and means for .re-passing stock from the barometric leg to and through a hydrocyclone.

11. The continuous process involving de-dirting of a. liquid'suspension of paper-making constituents en route to a paper-making apparatus, which comprises establishing and maintaining a primary de-dirting station made up of a plurality of hydrocyclones operating in parallel and each with a base discharge outlet and an apex discharge outlet, feeding the suspension tangentially into each hydrocyclone, spinning the suspension in each hydrocyclone with sufficient force to segregate the suspension into two fractions of which one is an acceptable fraction that is emitted through the base outlet while the other is a rejectable dirt-rich fraction, emitting as a spray the dirt-rich fraction through the apex outlet of each of said hydrocyclones into a non-submerged spray-receiving area of an expansion zone, establishing and maintaining in a single closed gas-separation tank a collected body of liquid, establishing and maintaining continuous communication between each of said sprayreceiving areas and said single gas-separation tank above the level of the body of liquid therein, continuously applying from an exterior power-operated vacuumproducer vacuum induced suction to the gas-separation tank above the level of the liquid therein and through the communication between the tank and the sprayreceiving areas to the spray-receiving areas and thence to the interior of each of the hydrocyclones to constantly suck air from the core of the hydrocyclones, through the spray-receiving areas into and from the gas-separation tank, establishing and maintaining a secondary de-dirting station made up of at least one hydrocyclone having a base discharge outlet and an apex discharge outlet, pumping liquid discharged from said spray-receiving areas and from the collected body in the gas-separation tank from a level below that of the body to the secondary de-dirting station to ensure delivery of the liquid to the secondary de-dirting station at constant pressure and volume, feeding the last-mentioned liquid tangen tially into the secondary hydrocyclone and spinning it with sufiicient force to segregate the suspension into two fractions of which one is an acceptable dirt-poor fraction that is emitted through the base outlet while the other is a rejectable dirt-rich fraction that is emitted through the apex outlet, and conveying the acceptable fraction from the base outlet portion of each of said hydrocyclones to a place of its use.

12. Apparatus for de-dirting paper-making stock, which comprises a primary cleaning station having a plurality of hydrocyclones connected in parallel, each ofsaid hydrocyclones having a base discharge outlet and an apex discharge outlet, means for feeding liquid suspension of paper-making constituents into each hydrocyclone, pump means in said feeding means for spinning such suspension in each hydrocyclone with sutficient I force to segregate two fractions in the hydrocyclone and to discharge a rejectable dirt-rich fraction from the apex outlet thereof and an acceptable dirt-poor fraction from the base outlet thereof, expansion chamber means associated with the apex outlet of each of said hydrocyclones, a single closed gas-separation tank having a body of collected liquid disposed therein during operation, means providing communication between said expansion chamber means and the interior of said gas-separation tank above the liquid level therein, power-operated vacuum-producing means, means connecting said vacuumproducing means with said gas-separation tank above the level of the collected liquid therein for continuously applying suction to the tank and to said expansion chamber means and said hydrocyclones for drawing air from the hydrocyclones, the expansion chamber means and said gas-separation tank, a secondary hydrocyclone station having at least one hydrocyclone with a base discharge outlet and an apex discharge outlet as well as a feed inlet, a pump means disposed at an elevation below said gas-separation tank, means connecting the lower portion of said tank and said expansion chamber means with said pump means, and means connecting said pump means to the feed inlet of said last-mentioned hydrocyclone, whereby constant pressure and constant volume delivery of liquid to said last-mentioned hydrocyclone is ensured.

References Cited in the file of this patent UNITED STATES PATENTS 1,520,588 McRae Dec. 23, 1924 2,312,706 Freeman Mar. 2, 1943 2,377,5M Samson et al. June 5, 1945 2,528,032 Caudler et al Oct. 31, 1950 2,614,656 Clark et al Oct. 21, 1952 2,642,950 Clark et al. June 23, 1953 2,685,937 Clark et al Aug. 10, 1954 2,717,536 Clark et al Sept. 13, 1955 2,816,490 Boadway Dec. 17, 1957 2,849,930 Freeman Sept. 2, 1958 2,878,934 Tomlinson Mar. 24, 1959 

